The present invention relates to a lubricating composition usable for lubricating an interface between a tire and a safety support mounted on a wheel rim within said tire, and a mounted assembly for an automobile provided with said lubricating composition. The invention relates to the lubrication between the support and the tire when traveling on a flat tire, following a drop in inflation pressure within said tire.
In order, when traveling at reduced or zero pressure of a tire, (referred to as traveling on a flat tire), to delay the deterioration due to heating of the zones of friction between various parts of the inner face of the tire, it has been attempted in the past to provide the inner face of the tire with a lubricating composition which is supposed to reduce the friction between these various parts of the tire.
These compositions are essentially composed of an aqueous lubricating agent, a thickening agent intended to increase the viscosity of the lubricating agent so as to minimize the flowing of said lubricating agent due to the weight when the vehicle is at rest or is traveling with its tires inflated, and a surfactant.
French patent specification FR-A-2 100 803 mentions such lubricating compositions for tire/tire lubrication. Each of the lubricating agents described in this document comprises water in a majority proportion and, in a minority proportion, a compound for lubrication such as a silicone oil, ethylene glycol or glycerine. In the example of embodiment mentioning glycerine, the latter is present in the lubricating agent and in the lubricating composition in volume fractions of approximately 30%, compared with 70% for water. Hydroxy-ethylcellulose is mentioned as thickening agent.
It will be noted that this high volume of water is intended, on one hand, to reinflate by volatilization the tire when traveling on a flat tire and to reduce to a certain extent the stresses of which the sidewalls of the tire are the seat, and, on the other hand, to optimize the foaming effect of the surfactant used when traveling on a flat tire.
French patent specification FR-A-2 397 453 and Japanese patent specification JP-B-83/30 000 also mention a lubricating composition for tire/tire lubrication which is intended to reduce the friction between the upper and lower parts of deflated sidewalls. The lubricating agent of the composition applied to the sidewalls of the tire comprises water in a majority proportion and ethylene glycol in a minority proportion, as in document FR-A-2 100 803. The lubricating composition comprises, as thickening agent, a polyethylene oxide and a polysaccharide, and it furthermore comprises a fibrous filler of cellulose type.
More recently, attempts have been made to improve the endurance of mounted assemblies, under conditions of travel at reduced or zero inflation pressure, by providing a safety support which is mounted on the wheel rim so as to be able to support the tread of the tire in the event of a drop in the inflation pressure. Mention may be made of French patent specification FR-A-2 746 347 for the description of such a support.
In this context, support/tire lubricating compositions were tested which are specifically intended to reduce the friction between said support and the inner face of the tire surrounding the support, these compositions conventionally being applied to the inner face of the tire, prior to the mounting thereof on the rim, and under conditions of travel on a flat tire and of load which are more severe and over periods which are distinctly superior to those relating to the prior tests without safety support.
As lubricating composition for support/tire lubrication, mention may be made for example of a composition the lubricating agent of which is based on polyalkene glycols and ethoxylated nonylphenol, and a thickening agent.
Such a composition imparts satisfactory endurance when traveling on a flat tire to the mounted assemblies incorporating it. However, one major disadvantage of this composition lies in the presence of the ethoxylated nonylphenol, which is a product that irritates the skin and eyes.